The invention pertains generally to tools and particularly to a thermic device and technique for cutting or removing an oxidizable material.
Many thermic techniques and devices rely on oxidation at elevated temperatures to cut or remove metals from a work piece. An early technique utilizes an oxyacetylene flame to locally preheat a spot on a metal surface to incandescene and a jet stream of a gas mixture of acetylene and mostly oxygen to oxidize and remove the oxide products of the combustion. Although this technique is moderately fast and efficient, it has several disadvantages arising from its requirement of large amounts of acetylene and oxygen gas which have to be supplied under high pressure and heavy metal containers. The containers consitute a serious hazard, particularly, in areas which are subject to bombardment or fire because an explosion or fire may cause them to explode with great force, scattering metal fragments for long distances. Another disadvantage is that the flame is not hot enough for many applications.
An alternative to the oxyacetylene technique which avoids its disadvantages is referred to as the arc-oxygen technique in which an electrode and the metal work piece are connected to a power source, a small area on the metal surface is heated by an electrical arc formed between the electrode and the metal work piece, and a jet stream of essentially oxygen oxidizes and removes the oxidation products from the work piece. Usually the oxygen is delivered and directed by a metal tubing which also serves as the electrode. Since the electric arc heats both the electrode and part of the work piece, the electrode is consumed and therefore the delivery tube of the arc oxygen cutter must constantly be replaced.
In order to improve the life of the tube the composition of the electrodes has been varied considerably. For example, U.S. Pat. No. 2,398,427 by Ernst Hediger, issued on Apr. 16, 1946 discloses a tube comprising a nonmetallic refractory metal with a sleeve made from metal with a high melting point, for example aluminum, nickel, brass or iron, and U.S. Pat. No. 2,802,930 by Bela M. Ronay, issued on Aug. 13, 1957, discloses an electrode fabricated from a material comprising cast iron, aluminum and silicon. A recent innovation, disclosed in U.S. Pat. No. 3,646,306 by Edwin W. Olds issued on Feb. 29, 1972, utilizes a thin wall tube with a wire-like structure at the center of the tube which becomes the electrode instead of the tube. The wire-like structure comprises carbon or graphite in a polymeric binder; so that, the electrode is flexible and can be continuously fed to the tip of the cutting torch. Aluminum or magnesium can be added to increase the temperature of the arc over that produced by the pure carbon or graphite electrode.
Other problems associated with thermic techniques or devices utilizing oxidation are temperatures that are too low for some applications and the requirement that an arc must always be present for the successful operation of the technique or device. The devices and methods, shown in U.S. Pat. Nos. 4,069,407 and 4,182,947 by Jerome S. Brower issued on Jan. 17, 1978 and Jan. 8, 1980 utilize the thermite reaction consisting of 8 moles of aluminum plus three moles of iron oxide to produce 4 moles of aluminum oxide plus nine moles of molten iron. The reaction is extremely exothermic, releasing 758,000 calories per gram molecular weight. This reaction is produced by passing a high-velocity stream of oxygen past steel rods and rods made from aluminum, magnesium, titanium, or alloys thereof located in a steel tube. While this approach produces high temperatures and a self-sustaining burn which allows cutting or removing nonconductive materials the problem of the tube being consumed remains unsolved.
Although the temperature produced in the Brower patents is extremely high, it should be higher for some applications. For example munition demilitarization requires the cutting to be faster than the heat transferred through the metal casing; so that, the propellant or explosive is combusted in a container opened to the atmosphere rather than in a closed container. Thus the cutting speed determines, to a large degree, the safety.